Recent user demands for high speed and multimedia communications have resulted in the need for high speed local area network (LAN) interconnection capability beyond local premises, integrated multimedia communication facilities for local premises and efficient inter-sites multimedia communication facilities. Particularly, there is a great need for high speed interconnection capability between LANs located in different sites.
Japanese Application 63-169849 discloses a broadcast communication control system operation under a conventional packet switching mode using a virtual circuit system. According to Japanese Application 63-169849 each exchange office has a memory in which information about the relationship between logic channel numbers and broadcast call identification numbers are stored. A logic channel number identifies for each exchange office the broadcast number identifies for each exchange office the broadcast paths of data in the form of broadcast cells to be transmitted from broadcast terminals to a plurality of reception terminals as broadcast communication destinations. A broadcast call identification number identifies a broadcast call.
The system disclosed by Japanese Patent application 63-169849 writes an identification number used for the broadcast call into a header of a broadcast packet so as to transfer the thus written number to a packet transfer network. The packet transfer network performs the relocation of a header only with respect to defined logic channels for output to outgoing lines, carries out conversion of the header to another header and transfers the header and the associated packet to each of the outgoing lines. In each exchange office, so as long as the logic channel numbers are defined in the memory as being related to broadcast call identification numbers with respect to the outgoing lines, a desired logic channel number at an outgoing line to which a broadcast package is to be transferred is obtained from the memory. Thus, a broadcast package may be delivered to a desired outgoing line.
In the system disclosed in Japanese Patent Application 63-169849 first the broadcast call identification number for the broadcast call is obtained from the logic channel number in each exchange office. The broadcast call identification number is then written into the header of the broadcast packet. Thereafter, the logic channel number for the outgoing line is determined from the broadcast call identification number thus changing the incoming logic channel number to the logic channel number for the outgoing line. Therefore, when the transfer of data at high speed is made in the conventional system the data exchange processing becomes more complicated being that at least two different processes must be performed. This increases the overhead of the exchange office thereby reducing its throughput. The overhead is defined as the number of required steps that must be performed in preparation for performing a desired step. Therefore, high speed interconnection of LANs located in different sites is not possible with the conventional systems.